2道prep求解

pocahontas

106.  11122-!-item-!-187;#058&007588

If a certain sample of data has a mean of 20.0 and a standard deviation of 3.0, which of the following values is more than

2.5 standard deviations from the mean?

 

 

(A) 12.0

(B) 13.5

(C) 17.0

(D) 23.5

(E) 26.5

<A>

142.  14580-!-item-!-187;#058&010013

The rate of a certain chemical reaction is directly proportional to the square of the concentration of chemical A present and inversely proportional to the concentration of chemical B present.  If the concentration of chemical B is increased by 100 percent, which of the following is closest to the percent change in the concentration of chemical A required to keep the reaction rate unchanged?

 

 

(A) 100% decrease

(B) 50% decrease

(C) 40% decrease

(D) 40% increase

(E) 50% increase

<D>

怎麼算都怪怪的

tangjinxiong

106，20-3*2.5=12.5

20+3*2.5=27.5

A不在这个范围内。

tangjinxiong

142，是怪怪的~

设这个rate为x，A^2为10，B为10，那么x：A^2=1：10；x*B=10.

现在B变为20，x就变为0.5，A^2变为5.

为了让x回到1，A^2必须回到10，那么A^2要增长100%，A要增长30+%，所以选D。